This invention relates to an adjustment device for a hydraulic shock absorber that can be used on any type of vehicle and particularly on all-terrain vehicles.
European patent EP 0 237 085 describes a hydraulic shock absorber comprising an adjustment device mounted between the shock absorber body and a monoblock fluid reservoir connected to the upper part of the cylinder forming the shock absorber. The shock absorber adjustment device is located on the junction between the reservoir and the shock absorber, and can be used to adjust the shock absorber compression force by means of two knurled wheels, without disassembling the shock absorber. Actions on the knurled wheels adjust expansion and compression of the shock absorber. However, this device is not capable of making different adjustments for low and high displacement speeds of the shock absorber piston. Furthermore, this device puts the adjustment means into communication with either the piston or the reservoir, through two pipes. This device also comprises a large number of parts and it is difficult to assemble.
International patent application WO 98/03361 deposited by the applicant also describes a hydraulic shock absorber system comprising a shock absorber and a reservoir connected through a pipe to the upper part of the cylinder in which the shock absorber piston is located. The system comprises shock absorber adjustment means located on the reservoir, for low and high speeds. However, this device comprises many parts and the reservoir has to be disassembled to adjust the shock absorber for high speeds.
Therefore, the purpose of this invention is to overcome the disadvantages of prior art by proposing an adjustment device with a simple design that will enable separate adjustment of the shock absorber for low and high piston displacement speeds, this adjustment being made without disassembling the shock absorber and without the use of special tools.
This purpose is achieved by the fact that the device according to the invention comprises a monoblock head designed to be fitted with firstly a cylinder containing the shock absorber piston, and secondly with a oil reservoir and adjustment means for low shock absorber piston displacement speeds and for high shock absorber piston displacement speeds, the monoblock head comprising a duct enabling oil circulation between the shock absorber and the reservoir, in which the low speed adjustment means and the high speed adjustment means are assembled such that their axes of symmetry are coaxial with the duct.
According to another feature, the low and high speed adjustment means are assembled in the monoblock head through a cavity on the duct, such that they define two different paths for passage of shock absorber oil to the reservoir depending on the displacement speed of the shock absorber piston, a first path being used by the oil during low speeds and a second path being used during high speeds.
According to another feature, shock absorber high speed adjustment means comprise firstly a compression valve assembled so that it slides coaxially on a first end of a first screw assembled so that it is adjustable in the duct, and secondly elastic means assembled on the first screw exerting a determined pressure on the compression valve when it is assembled on the first screw, such that the compression valve tends to move away from the first screw to define a second oil path as a function of the oil pressure exerted on the compression valve.
According to another feature, the shock absorber low speed adjustment means comprise firstly a second screw comprising a needle with a determined shape, assembled adjustably inside a coaxial drilling in the first screw, this drilling comprising a first section with determined dimensions exceeding the dimensions of the second screw, a second section with determined dimensions smaller than the dimensions of the second screw, these two sections being attached through a third section with a determined shape complementary to the shape of the needle in the second screw, and secondly means of draining oil back to the reservoir, formed on the compression valve and the first screw, to define the first path.
According to another feature, the elastic means consist of Belleville washers mounted in opposition.
According to another feature, the compression valve is formed of a hollow cylinder comprising two rings, between which there is at least one radial orifice forming means of draining oil to the reservoir.
According to another feature, the first screw consists of a hollow cylinder comprising at least one radial orifice in its first end forming means of draining oil to the reservoir, and a thread on its outside surface for adjusting the pressure of the elastic means on the compression valve.
According to another feature, the first and second screws comprise means of identifying the shock absorber setting comprising firstly at least one notch on the outside surface of the second screw parallel to its axis of symmetry, and secondly a radial slot on the first screw in which a ball and an elastic means are assembled, such that the ball cooperates with a notch in the second screw.
According to another feature, the needle in the second screw and the third drilling section in the first screw is in the shape of a truncated cone.
According to another feature, the first and second screws comprise means of adjusting them using conventional tools such as a spanner and/or a screwdriver.
According to another feature, the outside surface of the compression valve comprises at least one notch parallel to its axis of symmetry.
According to another feature, purge means are located on the monoblock head vertically above the reservoir attachment area and lead into the duct through a cavity.
Other special features and advantages of this invention will become clearer after reading the following description with reference to the attached drawings.